The present invention relates to a synchronous drive belt designed for improved tooth formation. More specifically, the present invention is directed toward a fabric covering layer for the synchronous drive belt for improved tooth formation.
Conventional synchronous drive belts have teeth placed at right angles to the belt mid-circumferential line. Such belts are well illustrated in U.S. Pat. Nos. 4,108,011 and 4,690,664. In these known prior art belts, the whole tooth engages with a corresponding pulley cavity at the same time.
U.S. Pat. No. 5,209,705 discloses a synchronous drive belt with at least two transversely adjacent rows of teeth, having centerlines, uniformly spaced apart in the longitudinal direction by a pitch length and extending obliquely to the longitudinal directional. The teeth in the transversely adjacent rows are at oppositely balanced angles and the centerlines of said adjacent teeth are offset from each other by a distance of from 10% to 90% of the pitch length. Such belts are known in shorthand terminology as helical-offset-tooth belts or HOT belts.
Prior art conventional belts and helical-offset-tooth belts of U.S. Pat. No. 5,209,705, for the purpose of wear resistance, are provided a stretchable fabric material on the outer surface of the belt teeth. Known abrasion resistance fabrics employed in the art are cotton, cotton-nylon blend, nylon, aramid, aramid-rayon blend, acrylic, acrylic-rayon blend, polyester, polyester-cotton blend and rayon. The selected fabric preferably has a thermal stability up to at least 500xc2x0 F.
U.S. Pat. No. 5,645,504 discloses the use of a knitted fabric with a 1xc3x971-rib construction for use in conventional synchronous belts of the first type previously described. The selected fabric has a pleated structure allowing stretch in a direction transverse to the knitted ribs. The fabric is stretched, in use, from about 15% to about 200%. During formation of the belt, the ribs of the fabric are oriented to extend transverse to the belt direction and aligned with the teeth. U.S. Pat. No. 5,545,097 discloses a tire belt with a resorcinol-formalin-latex (RFL) solution treated facing fabric. The facing fabric is a woven fabric with the warp threads running transverse to the belt direction, aligned with the teeth, and the weft threads running in a lengthwise direction. The fabric is plain weave, twill weave, satin weave or the like. The fabric is initially shrunk to about fifty percent of the original width, immersed in RFL solution, squeezed, and then dried. If necessary the fabric may by dipped in RFL again to obtain a desired 30-50% solid RFL attachment to the fabric.
U.S. Pat. No. 5,609,541 discloses a tooth facing fabric treated with a rubber composition in which hydrogenated acrylonitrile-butadiene rubber is mixed with N,Nxe2x80x2-m-phenylenedimaleimide.
Single directional scaffold construction fabric, permitting stretch in the single direction, has also been employed as abrasion resistant fabric in synchronous belt constructions, as disclosed in U.S. Pat. No. 5,501,643.
While all the prior art fabrics provide acceptable abrasion resistance for conventional belts with transversely extending teeth, greater tooth profiling can be achieved by use of a bi-directional stretch fabric as further disclosed in the present invention. Such a fabric is especially suited for belts of the type disclosed in U.S. Pat. No. 5,209,705.
For the inclined centerline teeth of the HOT belt, the surface face of the teeth varies in both the transverse and longitudinal direction of the belt. When a single directional stretch fabric is laid with the weft threads parallel to the longitudinal of the belt, no consideration is provided for the variation of the belt surface in the transverse direction. The inventive use of a bi-directional fabric as disclosed herein provides for surface variation in both directions, and enables better tooth profiling. The inventive aspect of the disclosed invention is also applicable to non-inclined teeth for synchronous drive belts.
The present invention is directed toward improved tooth formation in belting. The disclosed invention is applicable in tooth formation of conventional straight toothed belts and helically-offset tooth belts.
The disclosed fabric is stretchable in both directions, and may have greater stretch characteristics in one direction than in the opposing direction.
The disclosed invention is obtained by providing the belting with an outer tooth reinforcement layer of a woven bi-directional stretch fabric. The woven fabric, comprising warp and weft threads, is of a scaffold construction.
Each warp and weft thread of the bi-directional stretch fabric is provided with a core yarn about which is helically wrapped at least one yarn, permitting relative movement of the core yarn within the wrap of the second yarn.